Embodiments of the present disclosure generally relate to neurostimulation (NS) systems, and more particularly to systems and methods for closed loop spinal cord stimulation (SCS) controlling non-paresthesia stimulation of nerve tissue of a patient.
NS systems are devices that generate electrical pulses and deliver the pulses to nerve tissue to treat a variety of disorders via one or more electrodes. For example, SCS has been used to treat chronic and intractable pain. Another example is deep brain stimulation, which has been used to treat movement disorders such as Parkinson's disease and affective disorders such as depression. While a precise understanding of the interaction between the applied electrical energy and the nervous tissue is not fully appreciated, it is known that application of electrical pulses depolarize neurons and generate propagating action potentials into certain regions or areas of nerve tissue. The propagating action potentials effectively mask certain types of physiological neural activity, increase the production of neurotransmitters, or the like.
SCS devices apply electrical energy to the spinal cord. Conventionally, the SCS corresponds to a series of continuous pulses at around 50 Hz forming a “tonic waveform” to stimulate the nerve tissue of a patient inducing “paresthesia” (a subjective sensation of numbness or tingling by the patient) in the afflicted bodily regions. Inducing this artificial sensation replaces the feeling of pain in the body areas effectively masking the transmission of non-acute pain sensations to the brain.
Recently, SCS devices have begun using a non-paresthesia stimulation waveform such as a “burst waveform” to relieve pain symptoms within the afflicted bodily regions instead of the tonic waveform. The burst stimulation waveform has bursts of multiple stimulation pulses, and these bursts are separated by inter-burst delay periods in which no stimulation is applied. Unlike the tonic waveform, SCS using the burst waveform may not generate paresthesia. However, due to the lack of paresthesia, there may be a loss of patient feedback regarding the location and strength of stimulation. Due to this loss of patient perception, there may be a greater risk of over-stimulation when the NS system moves with respect to the spinal cord during movement of the patient.
During stimulation by the NS systems, evoked potentials are emitted from the stimulated nerve tissue. It has been proposed that the NS system may measure the evoked potential for a feedback mechanism to adjust the SCS. The evoked potential signals may be generated by neuronal transmembrane currents of neurons activated following or in response to the SCS. The evoked potential signals propagate within the population of sensory nerve fibers through subsequent orthodromic or antidromic propagation from the excitation site. SCS using the tonic waveform results in the simultaneous activation of multiple neurons, which generate a signal of sufficient amplitude for recording. However, SCS using the burst waveform may not simultaneously activate the multiple neurons. For example, during the burst waveform one or more neurons may be activated at different times. This can result in an evoked potential signal lacking coherent neuronal activation, which may hinder recording of the evoked potential and use of feedback mechanisms for closed loop adjustment of SCS.
A need exists to overcome the shortcomings of traditional recording of evoked potential signals generated from stimulation using burst waveforms.